This invention relates generally to power windows, and in particular an anti-pinch window control system in power windows in a vehicle.
In view of the significant convenience that they provide over manually operated windows, power windows have become a standard feature on most new motor vehicles. However, despite their consumer acceptance, power windows pose a risk of harm to objects inadvertently caught between the window and the sash as the window is closed. In view of the potential danger posed by power windows, certain government regulations dictate the maximum amount of force that may be applied by the electric motor in closing the window.
To prevent injuries from occurring, motor vehicles have been provided with anti-pinch safety systems that detect the presence of a foreign object pinched between the window and sash. Once a pinched object is detected, upward movement of the window is halted and the window is moved downward to free the object.
There are two types of safety systems in common usage, including the xe2x80x9cdifferentialxe2x80x9d type and the xe2x80x9cabsolute type. The differential type of safety system recognizes a pinched condition from a detected change in window velocity. As the window moves upward with a velocity measured by a sensor that detects the rotational rate of the electric motor. Generally the window is moved at a constant velocity. In a pinched condition, however, the velocity abruptly drops. The sensors can also detect changes in velocity over time, and in either case the anti-pinch safety system recognizes the pinched condition and reverses the upward travel of the window.
The absolute type of safety system recognizes a pinched condition when the applied motor torque exceeds a predetermined limit. The torque produced by the electric motor is generally proportional to the electric current drawn by the electric motor. In a pinched condition, the presence of a foreign object between the window and sash represents a frictional force that is opposite in direction to the applied motor torque. As a result, the electric motor draws additional current to compensate for the increased frictional force. The anti-pinch safety system monitors the current drawn by the electric motor and recognizes the pinched condition when the current exceeds a predetermined limit.
The prior art anti-pinch safety systems outlined above rely on pre-programmed limits in window velocity or electric motor torque to signal that pinched condition exists. The problem with these systems is that an abrupt load on the window can develop, which is not due to a pinched condition, but to other normal conditions, with the anti-pinch safety system halting window operation. For example, if the temperature changes, if ice forms on a window, if soda is spilled on the window, the load on the window, which translates to an additional frictional farce, can change abruptly without there being a foreign object between the window and the sash. Window loads can vary by as much as five times a pre-programmed pinch threshold rendering the prior art systems inadequate for many applications.
Accordingly, there is a significant need for compensating for abrupt load changes in an anti-pinch window control system that overcome the deficiencies of the prior art outlined above.